The present invention relates to wireless telecommunications systems and methods, and in particular to systems and methods for allocating transmission resources in wireless telecommunication systems.
Mobile communication systems have evolved over the past ten years or so from the GSM System (Global System for Mobile communications) to the 3G system and now include packet data communications as well as circuit switched communications. The third generation partnership project (3GPP) is developing a fourth generation mobile communication system referred to as Long Term Evolution (LTE) in which a core network part has been evolved to form a more simplified architecture based on a merging of components of earlier mobile radio network architectures and a radio access interface which is based on Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) on the uplink.
Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architectures, are able to support a more sophisticated range of services than simple voice and messaging services offered by previous generations of mobile telecommunication systems.
For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.
The anticipated widespread deployment of third and fourth generation networks has led to the parallel development of a class of devices and applications which, rather than taking advantage of the high data rates available, instead take advantage of the robust radio interface and increasing ubiquity of the coverage area. Examples include so-called machine type communication (MTC) applications, some of which are in some respects typified by semi-autonomous or autonomous wireless communication devices (MTC devices) communicating small amounts of data on a relatively infrequent basis. Examples include so-called smart meters which, for example, are located in a customer's home and periodically transmit data back to a central MTC server relating to the customer's consumption of a utility such as gas, water, electricity and so on. Smart metering is merely one example of potential MTC device applications. Further information on characteristics of MTC-type devices can be found, for example, in the corresponding standards, such as ETSI TS 122 368 V10.530 (2011-07)/3GPP TS 22.368 version 10.5.0 Release 10) [1].
Whilst it can be convenient for a terminal such as an MTC-type terminal to take advantage of the wide coverage area provided by a third or fourth generation mobile telecommunication network there are at present disadvantages. Unlike a conventional third or fourth generation mobile terminal such as a smartphone, a primary driver for MTC-type terminals will be a desire for such terminals to be relatively simple and inexpensive. The type of functions typically performed by an MTC-type terminal (e.g. simple collection and reporting/reception of relatively small amounts of data) do not require particularly complex processing to perform, for example, compared to a smartphone supporting video streaming. However, third and fourth generation mobile telecommunication networks typically employ advanced data modulation techniques and support wide bandwidth usage on the radio interface which can require more complex and expensive radio transceivers and decoders to implement. It is usually justified to include such complex elements in a smartphone as a smartphone will typically require a powerful processor to perform typical smartphone type functions. However, as indicated above, there is now a desire to use relatively inexpensive and less complex devices which are nonetheless able to communicate using LTE-type networks.
With this in mind there has been proposed a concept of so-called “virtual carriers” operating within the bandwidth of a “host carrier”, for example, as described in co-pending UK patent applications numbered GB 1101970.0 [2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5], GB 1101853.8 [6], GB 1101982.5 [7], GB 1101980.9 [8] and GB 1101972.6 [9]. A main principle underlying the concept of a virtual carrier is that a frequency subregion within a wider bandwidth host carrier is configured for use as a self-contained carrier, for example including all control signalling within the frequency subregion. An advantage of this approach is to provide a carrier for use by low-capability terminal devices capable of operating over only relatively narrow bandwidths. This allows devices to communicate on LTE-type networks, without requiring the devices to support full bandwidth operation. By reducing the bandwidth of the signal that needs to be decoded, the front end processing requirements (e.g., FFT, channel estimation, subframe buffering etc.) of a device configured to operate on a virtual carrier are reduced since the complexity of these functions is generally related to the bandwidth of the signal received.
There are, however, some potential drawbacks with some implementations of the “virtual carrier” approach. For example, in accordance with some proposed approaches the available spectrum is hard partitioned between the virtual carrier and the host carrier. This hard partitioning can be inefficient for a number of reasons. For example, the peak data rate that can be supported by high-rate legacy devices is reduced because high-rate devices can only be scheduled a portion of the bandwidth (and not the whole bandwidth). Also, when the bandwidth is partitioned in this way there can be a loss of trunking efficiency (there is a statistical multiplexing loss).
What is more, in some respects the virtual carrier approach represents a relatively significant departure from the current operating principles for LTE-type networks. This means relatively substantial changes to the current standards might be required to incorporate the virtual carrier concept into the LTE standards framework, thereby increasing the practical difficulty of rolling out these proposed implementations.
Another proposal for reducing the required complexity of devices configured to communicate over LTE-type networks is proposed in co-pending UK patent applications numbered GB 1121767.6 [11] and GB 1121766.8 [12]. These applications propose schemes for communicating data between a base station and a reduced-capability terminal device in an LTE-type wireless telecommunications system operating over a system frequency band. Physical-layer control information for the reduced-capability terminal device is transmitted from the base station using subcarriers selected from across the system frequency band as for conventional LTE terminal devices. However, higher-layer data for reduced-capability terminal devices (e.g. ATC user-plane data) is transmitted using only subcarriers selected from within a restricted frequency band which is smaller than and within the system frequency band. The terminal device is aware of the restricted frequency band, and as such need only buffer and process data within this restricted frequency band during periods where higher-layer data is being transmitted. The terminal device buffers and processes the full system frequency band during periods when physical-layer control information is being transmitted. Thus, the reduced-capability terminal device may be incorporated in a network in which physical-layer control information is transmitted over a wide frequency range, but only needs to have sufficient memory and processing capacity to process a smaller range of frequencies for the higher-layer data.
There are, however, some potential drawbacks with some implementations of the schemes proposed in GB 1121767.6 [11] and GB 1121766.8 [12]. For example, the scheduling flexibility available to the base station may be reduced because of the requirement to allocate resources to reduced-capability devices within a narrowed frequency band. Furthermore, where there is at least flexibility in selecting the reduced frequency band to be used, there can be a need for additional signalling between the base station and the reduced-capability terminal devices to negotiate (i.e. agree) the frequency range to be used. This is because the reduced-capability terminal device and the base station both need to know the narrowed bandwidth to be used such that the terminal device knows which part of the frame structure to buffer, and the base station knows to allocate resources for the reduced capability terminal device within this bandwidth.
Another proposal for reducing the required complexity of devices configured to communicate over LTE-type networks is proposed in the discussion document R1-113113 from Pantech submitted for the 3GPP TSG-RAN WG1 #66bis meeting in Zhuhai, China, 10 Oct. 2011 to 14 Oct. 2011 [12]. The proposal is for low-complexity terminal devices to be allocated a limited number of physical resource blocks as compared to a device with is fully LTE-compliant. This scheduling restriction means terminal devices can implement their turbo decoding function more simply, thereby reducing the processing complexity required.
However, while this can be helpful in reducing the processing capability required for turbo decoding, significant amounts of a device's processing requirements are associated with front-end digital signal processing functions prior to turbo decoding. Such front-end digital signal processing functions include, for example, FFT/IFFT (fast Fourier transform/inverse fast Fourier transform), channel estimation, equalization, digital filtering, etc.
Accordingly, there remains a desire for approaches which allow relatively inexpensive and low complexity devices to communicate using LTE-type networks.